GB2118354A

GB2118354A - Process and apparatus for the vitrification of radioactive waste solutions

Info

Publication number: GB2118354A
Application number: GB08306747A
Authority: GB
Inventors: Friedrich Kaufmann
Original assignee: Deutsche Gesellschaft fuer Wiederaufarbeitung von Kernbrennstoffen mbH
Current assignee: Deutsche Gesellschaft fuer Wiederaufarbeitung von Kernbrennstoffen mbH
Priority date: 1982-03-13
Filing date: 1983-03-11
Publication date: 1983-10-26
Also published as: BR8301242A; GB8306747D0; US4615833A; FR2523360B1; US4592898A; JPH0246118B2; DE3209250C2; BE896046A; GB2118354B; DE3209250A1; FR2523360A1; JPS58168997A

Description

1 GB 2 118 354 A 1

SPECIFICATION

Process and apparatus for vitrifying radioactive waste solutions Radioactive fission products produced liquid form in the first extraction cycle of a processing plant are usually vitrified since glass forms a mechanically stable product and holds the radionuclides very tightly together.

The highly radioactive fission product solution is usually fed from a storage container in measured amounts to the vitrification plant. This storage container is charged from a receiving container for the radioactive fission product solution.

The ofigases generated during the vitrification of the fission product solution in the melting furnace of a vitrification plant must be freed of the entrained dust particles and the like to prevent the potential blocking of lines and components. It is therefore customary to pass the offgas through an offgas scrubbing stage for removal of the dust particles. The offgas is scrubbed in this purification stage in counterflowwith a scrubbing solution in which the removed acids, dust particles and aerosols have accumulated.

The scrubbing liquid is conducted in a circulatory system to minimize the production of secondary radioactive waste. After a certain time, the circulat- ing scrubbing liquid is heavily contaminated and must be renewed.

It is an aim of the invention to create a process and apparatus forthe vitrification of fission product solutions, which has a simplified process cycle and in which waste scrubbing is less costly.

According to one aspect, the invention provides a process for vitrification of radioactive fission products present in liquid solution, which comprises metering the fission product solution from a feed container to a vitrifying plant and scrubbing the offgas generated during vitrification to remove entrained dust particles or the like by a scrubbing liquid in an offgas scrubber, wherein radioactive fission product solution is removed from the feed tank and fed to the head of the offgas scrubber to provide the 110 scrubbing liquid, the fission product solution is returned to the feed container after passing through the offgas scrubber, and the offgas from the vitrifying plant is conducted in counterflow through the offgas scrubber.

The process according to the invention provides for the use, as a scrubbing liquid, of the liquid fission product solution itself that is situated in the feed container. A separate scrubbing liquid, which represents additional secondary waste, is no longer necessary. The two process steps, metering of the fission product solution from the feed container and offgas scrubbing, are simplified significantly.

The offgas from the vitrification plant is preferably conducted into the feed container above the liquid level. From there, the offgas enters the offgas scrubber. This has the advantages that the offgas has already been subjected to a pre-scrubbing in the feed container before it reaches the offgas scrubber.

For the implementation of the process of the 130 invention the invention also concerns an apparatus for the vitrification of highly radioactive, liquid fission product solutions with a vitrification plant having a glass melting furnace, which is connected with a feed container for the liquid fission product solution via a metered conveyer system, and with a counterflow scrubber for scrubbing of the furnace offgas of the vitrification facility with a scrubbing liquid conducted in a circulatory system. To reduce the number of facility components, the discharge of the counterflow scrubber is connected with the feed container and a pipeline preferably provided with a metering and conveying device is arranged between the feed container and the head of the counterflow scrubber.

Thus, according to a second aspect, the invention provides apparatus for the vitrification of highly radioactive liquid fission products which comprises a vitrification plant having a glass melting furnace, a feed tankforthe liquid fission product solution connected thereto via a metering and feeding device, and a counterflow scrubber for scrubbing of the vitrification plant furnace offgas with the scrubbing liquid solution being recycled, wherein a drain outlet of the counterflow scrubber is connected to the feed container and a connection is arranged between the feed tank and the head of the counterflow scrubber.

For simplicity, the offgas scrubbing stage and the feed container for the fission product solution are preferably combined in this manner into one component.

In a preferred embodiment of the device according to the invention, the offgps line supplying the furnace offgas enters the feed container above the level of the liquid. The introduction of the offgas into the feed container is, due to structural considerations, more favourable than the introduction into offgas scrubbing column that is provided with a narrower cross-section.

In another preferred embodiment of the invention there is arranged in the feed container an air-pulse system immersed in the fission product solution. As a result of air pulses produced by this system it is possible to prevent the formation of sediments on the bottom of the feed container.

An embodiment of the invention will now be described by way of example with reference to the accompanying diagrammatic drawings.

A vitrification facility or plant 1 of generally conventional type has a glass melting furnace (not shown) which is raised to giass-melting temperature by a heater 2. The arrow 3 indicates the discharge of the molten glass with absorbed radioactive f ission products. Fritted glass is added to the vitrification plant 1 via an admixing opening (arrow 4) and the highly radioactive fission product solution is introduced in measured amounts through an inlet opening 5.

In a supply line 6 that connects the inlet opening 5 with a feed container 7, there is arranged a metering air-lift container 8 of a metering air-lift conveying device. Such air-lift conveying devices have proved themselves for the metered feed of radioactive fission product solutions. With these air-lift conveyor devices the conveying movement is brought about 2 GB 2 118 354 A 2 by bubbling air into a column of liquid. The supply of air occurs here through a line 9 at the lower end of the input line 6 arranged in the lower area of the feed container 7. The conveyance of the fission product solution by means of an air-lift is more reliable than with a pump since the air-lift has no moving parts.

This eliminates pump replacement that could poss ibly be required. No secondary waste is generated as a result of a contaminated pump and the possible exposure to radiation of the personnel during pump replacement is eliminated.

The fission product solution is supplied to the feed container 7 from a collecting tank (not shown) by pumps or by another air-lift system, via an inlet 10.

Claims

The level of the liquid inside said feed container 7 is 80 CLAIMS kept between two predetermined limits at all times. Into the feed container 7 there projects a pulsation pipe 11 into which the liquid is sucked by a reduced air pressure. The pressure in pipe 11 is then raised and the liquid is forced back out of the pipe 11 into the feed container 7. The cycle is then repeated. It is the purpose of this air-pulse system to prevent sedimentation in the feed container 7. Into the feed container 7 there also projects the lower end of a scrubbing column 12 having at its head a discharge 13 forthe scrubbed furnace offgas. The scrubbing column 12 is charged in its upper region with a scrubbing liquid taken via a metering line 14, provided with an air-lift container 15, from the liquid stored in the feed container 7. The air supply for this air-lift conveyance system is provided by an input line 16. The vitrification plant 1 has an ofigas line 17 that enters the feed container 7 above the level 18 of the liquid. The feed container 7 can be cooled or heated by means of a cooling or heating element 19. The mode of operation of the apparatus described above is as follows: The fission product solution to be vitrified is 105 supplied to the feed container 7 from a collector vessel (not shown). The level 18 of the liquid in the feed container 7 is monitored so that it will be at all times between two limit values. The supply line 6 is immersed into the fission product solution and the solution is introduced in measured amounts via the input line 6 into the vitrification plant 1 by means of the metering air-lift container 8 and the supply of air via the line 9. At the same time, fritted glass (arrow 4) is charged into the vitrification plant 1. Following the 115 sintering of the fritted glass, the radioactive fission products are bonded in the glass and periodically drawn off from the vitrification plant 1. The offgas generated during vitrification entrains radioactive dust particles and enters via the offgas line 17 into the feed container 7 above the level 18 of the liquid. The offgas then traverses the sc,ubbing column 12 from the bottom up in counterflow to the scrubbing liquid charged into the upper region, which liquid has been drawn off from the fission production solution stored in the feed container 7. While passing through the scrubbing column 12, the major portion of the dust particles, aerosols, and the radionuclides volatilized during vitrification are absorbed by the amount of fission product solution serving as scrubbing liquid. The contaminated scrubbing liquid flows back into the feed container 7. On leaving the feed container 7 it is partly returned again to the head of the gas scrubber 12 and partly via the input line 6 to the vitrification plant 1. If in the fission product solution in the feed container 7 there accumulate components which, due to continuous gas scrubbing, are in excess of admissible limit values and which cannot be absorbed by the fused glass, a portion of the scrubbing solution is drawn off for additional processing. The level of the liquid in the feed container 7 is restored via the input line 10.

1. A process for vitrification of radioactive fission products present in liquid solution, which comprises metering the fission product solution from a feed container to a vitrifying plant and scrubbing the offgas generated during vitrification to remove entrained dust particles orthe like by a scrubbing liquid in an offgas scrubber, wherein radioactive fission product solution is removed from the feed tank and fed to the head of the offgas scrubber to provide the scrubbing liquid, the fission product solution is returned to the feed container after passing through the offgas scrubber, and the offgas from the vitrifying plant is conducted in counterflow through the offgas scrubber.

2. A process according to Claim 1, wherein the furnace offgas is conducted from the vitrification plant into the feed container and from there through the offgas scrubber.

3. Apparatus for the vitrification of highly radioactive liquid fission products which comprises a vitrification plant having a glass melting furnace, a feed tankfor the liquid fission product solution connected thereto via a metering and feeding device, and a counterflow scrubber for scrubbing of the vitrification plant furnace offgas with the scrubbing liquid solution being recycled, wherein a drain outlet of the counterflow scrubber is connected to the feed container and a connection is arranged between the feed tank and the head of the counterflow scrubber.

4. Apparatus according to claim 3, wherein the connection is a pipeline with a metering-conveying device.

5. Apparatus according to claim 3 or 4, wherein an offgas line supplying the furnace offgas to the feed container enters above the level of the liquid.

6. Apparatus according to Claim 3,4or5, wherein an air-pulse system is arranged in the feed container and is immersed in the fission product solution.

7. A process for vitrification of radioactive fission products present in liquid solution, substantially as hereinbefore described with reference to the drawing.

0 4_ 1 A i 3 GB 2 118 354 A 3

8. Apparatus for the vitrification of highly radioactive liquid fission products, substantially as hereinbefore described with reference to the drawing.

Printed for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1983. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.